This invention relates to a low-noise television system having means for suppressing increase of noise as maintaining improved picture quality in television broadcast transmission and reception.
As described, for example, in the report of Sudo et al, "Technology for High-Picture Quality of Color TV Receiver", Toshiba Review, Vol. 41, No. 6 (1986) pp. 500-503 and the report of Toyoda, "Trend of Color TV Circuit of '86 Type", TV Technique (Terebi Gijutzu), Extra number of Sept. 1986 (No. 420) pp. 21-22the luminance component of a television signal is transmitted from a broadcasting station in a relatively uniform characteristic up to a range above 4 MHz and a color subcarrier is superimposed therewith at a position of 3.58 MHz. In a modern television receiver, the luminance and chrominance signal components are completely separated by a comb-filter and the luminance signal component is processed in a uniform characteristic in order to avoid undesirable phoenomena, such as cross-color. In such receiver, the bandwidth of luminance signal expands much more than that of the conventional receivers and this results in incease of noise. Therefore, picture quality control function is also provided to make it adjustable for making the noise unnoticeable in some receiving conditions.
As a measure of expanding the usable bandwidth of luminance signal as maintaining the noise suppressed, it is considered to pre-emphasize the luminance signal amplitude in the transmitter and to de-emphasize it in the receiver. However, excessive emphasis for sufficient noise suppression can cause undesirable overmodulation.